Measurements of the leptonic branching ratios with OPAL

Abstract

The branching ratio of the τ¯→e¯v¯evτ decay and the radiative tau decay τ→u¯v¯uvτγ have been measured with the OPAL detector at LEP. A branching ratio of 0.1778±0.0010±0.0009 was obtained for the τ¯→e¯v¯evτ decay mode and (3.0 ± 0.4 ± 0.5) × 10−3 for the τ¯→u¯v¯uvτγ decay mode for photon energies above 20 MeV in the tau rest frame.